I had the same roommate all through college. We lived in a house with a bunch of other guys and we were used to girlfriends staying over from time to time.
One night I came home to find my roommate and his girlfriend, Michelle, asleep in his bed after a night of partying. I had some reading to do, so I took a quick shower, got into some boxers, crawled into bed and turned on the reading light.
After a while, the book got boring and I got the urge to play with myself. My roommate's bed was only four feet away, and they were both gently snoring, so I figured all was clear.
I slipped out of my shorts and got to work. I left the light on, since I like to look at my penis while I jerk it. It didn't take me long to get hard, but I was in no hurry to orgasm. There was something exciting about lying naked and erect only four feet away from my roommate's girlfriend, and I wanted to enjoy it.
After a few minutes of long, hard, slow strokes, I glanced over to my left. To my shock, Michelle's eyes were open and looking straight into mine. At first I froze, not knowing how she would react. There was no denying what I was doing, so I was pretty much at her mercy. We said nothing, however, and she didn't look away. So, I slowly continued, only this time very slowly and deliberately. I started at the head and rubbed all the way down the shaft, stretching my dick to its full length and pulling my balls down as far as they would go. When I got to the base, I squeezed hard so the blood would swell the head of my cock. I shave as well, so there was nothing blocking her view.
I watched her eyes go from my eyes to my cock, back and forth as I put on my little show. She never said a word, but she clearly didn't mind. I wondered how my dick compared to my roommate's. I had seen him naked before in the communal showers at school and soft we were basically the same size. Hard, I am 6.5' and nearly 6' around, and I think a part of me hoped Michelle was looking at the bigger of the two cocks in the room.
The show continued for a few minutes until, despite my efforts to delay it, I could feel my orgasm coming on. The head of my cock was now purple and huge, shining with precum that I smoothed around for her. I looked at her as if to say, 'Do you want to see me cum?' and she nodded quietly. I laid my head back and within seconds I erupted into an orgasm of nearly seismic proportions. I couldn't make any sound, for fear of waking my roommate, but my body went into spasm like never before. Ropes of cum shot up onto my chest and even my face. It seemed to last for minutes. Finally, I looked over at Michelle. She looked at me for a few seconds, rolled over and went back to sleep.
The next morning, they were up first and I met them in the living room as they were heading out for breakfast. Michelle and I exchanged a polite 'good morning' and said nothing. We have never talked about it. They got married and have two kids now. I wonder if she ever thinks about it.